In known machines for thermal deburring particularly referred to, a chemical process takes place under the influence of heat. In thermal deburring, the material to be removed is oxidized, or combusted, with oxygen. The heat shock necessary for deburring is generated by the combustion of a mixture of combustion gas and oxygen; hydrogen or natural gas, such as methane, may be used as the combustion gas. In order to be able to liberate the necessary energy, the gas mixture must be compressed before being ignited. This is generally accomplished with the aid of metering cylinders and gas injection cylinders. In known systems, the mixing and ignition of the combustion gas and oxygen mixture is effected in a separate mixing block.
Such known mixing apparatus comprise a housing, in which the mixing chamber and igniting device are located. This mixing chamber is connected via a relatively long duct with the work chamber, the duct serving to protect the valves disposed between the mixing block and the metering device when the highly compressed gas ignites. The combustion temperature of the gas is in the range from 2500.degree. to 3500.degree. C. The pressures of the combustion gas and oxygen mixture occurring in the work chamber are on the order of up to 60 bar when the work chamber is filled.
In known systems for thermal deburring, the workpiece that is to be trimmed is placed upon a closing plate, which is then driven upward from below against the cylindrical deburring chamber, so as to form with the deburring chamber a work chamber that is sealed against high pressures and temperatures.
In another form of embodiment according to German published patent application DE-OS No. 32 04 995 (to which U.S. Pat. No. 4,487,576 corresponds), the necessity for a mixing block is avoided by providing that the wall surrounding the work chamber is an inner chamber wall, surrounded by an outer chamber wall that is axially slidable relative to it; during the process of filling the work chamber with gas, the work chamber is closable by means of the outer chamber wall, while during the ignition process it is closable by means of the inner chamber wall. The inner chamber wall may have bores for delivering both the combustion gas and the oxygen, which flows into the work chamber when the outer chamber wall is closed relative to the closing plate, before the inner chamber wall is closed. The ignition of the mixture of combustion gas and oxygen then takes place in the work chamber. This construction is intended to counteract the corrosive effect of the combustion gas and oxygen mixture on the delivery means of the mixture when it is ignited; however, it represents an additional expense.
As noted above, the known apparatus have the disadvantage that the mixture of combustion gas and oxygen, when it ignites, not only causes the deburring of the workpieces being trimmed, but also has a corrosive effect upon the parts with which it comes into contact either during ignition or during the trimming operation. In both instances mentioned above, this applies to the inner wall of the work chamber, and in the case of an apparatus having a mixing block and a supply duct, it applies to both the supply duct and that part of the mixing block into which the ignition process extends. The supply duct is particularly imperiled because it is curved or bent at an angle at at least one point. Countermeasures against this corrosive effect are therefore in order for the apparatus of the type discussed above.